Conventionally, rubber hose has been produced by covering a mandrel as a core with a material of a rubber hose, and pulling out the mandrel after vulcanization. A mandrel for forming a rubber hose is produced by extruding a molten thermoplastic resin from an extruder via a Long Land Die and cooling thereof. By utilizing, during such process, only an ejecting force from an extruder without using a hauler, a strain does not occur easily inside the obtained mandrel (JP-A-2000-108191). A mandrel for forming rubber hose, which is produced in this way, can be used many times. This is because such mandrel for forming rubber hose shows markedly small changes in outer diameter even when heated during production of rubber hose.
JP-A-2000-334748 discloses a mandrel made from a thermoplastic polyester elastomer containing the following components A, B and C, and also satisfying the condition D.    A: aromatic dicarboxylic acid component    B: short chain glycol component    C: polyether glycol copolymer component having a molecular weight of 500-4000 and two or more different kinds of alkylene units, which is represented by the following chemical formula:HO—[(R1-O)a—(R2-O)b—(R3-O)c]n—Hwherein            (1) R1, R2 and R3 each show an alkylene unit having 2 to 10 carbon atoms wherein R2 is different from R1 and R3, and R1 may be the same as or different from R3,        (2) a, b and c are each an integer of not less than 0 satisfying a+b+c≧2, provided that at least two of a, b and c are not less than 1,        (3) n is an integer of not less than 2 and a number capable of achieving the molecular weight of the polyether glycol copolymer component of 500-4000.            D: thermoplastic polyelastomer contains an alkylene unit having a quaternary carbon atom, in a proportion of less than 10 wt % of the total weight of the polyether glycol component.
The mandrel made from the above-mentioned material has the water resistance, heat resistant aging property and chemical resistance same as those of conventional mandrels, and is superior in flexibility at low temperature and heat resistance and thermal cycle resistance sufficient for use at a high temperature.
However, even the aforementioned mandrel cannot be used forever, and as the number of use increases, the outer diameter changes. As a result, production of a rubber hose having a uniform thickness may be unavailable and scar may be produced in the inside of rubber hose. Generally, therefore, a mandrel used for a certain period is discarded before the above-mentioned problem occurs.
In recent years, effective utilization of resources has become a hot topic due to the penetration of recycling activity. The thermoplastic resin capable of becoming a material of mandrel needs to be positively recycled. JP-A-2000-326407 discloses a method of forming resin articles after use into a thin film, which comprises casting recovered product mainly containing thermoplastic resins in one or two extruders and extrusion forming the resin using two or more dies into a sheet. The aforementioned method effectively uses resources and achieves recycling. However, reuse, such as reusing a mandrel as a mandrel has not been achieved. Examples of reuse include fractional recovery of copper wire and aluminum wire from used electric cable, mixing with a new material, performing sequential molding to produce a wire rod for use again as an electric cable and the like. However, an example of reuse of a mandrel for forming a rubber hose has not been known.